Today, high-end frequency standard references have relatively high cost, large size, high power consumption, etc. The fast deployment of devices and/or systems such as, but not limited to, global positioning systems (GPS) and/or portable GPS systems, cellular systems and/or portable cellular phones and/or small size and low cost cellular base stations, fast telecommunications systems and other high-speed communication links, which employ very high modulation frequencies require stable, precise and accurate frequency standard reference which have small size, low cost and low power consumption. More information on these issues can be found in the following references: M. A. Sturza, “GPS navigation Using Three Satellites and a Precise Clock,” in Global Positioning System, vol. 2. Washington, D.C.: Institute of Navigation, 1984, pp. 122-132; J. Murphy and T. Skidmore, “A low-cost atomic clock: impact on the national airspace and GNSS availability,” in Proceedings of ION GPS-94; 7th International Meeting of the Satellite Division of the Institute of Navigation. Salt lake City, Utah, 1994, pp. 1329-1336; H. Fruehauf, “Fast “direct-P(Y)” GPS signal acquisition using a special portable clock,” in 33rd Annual Precise Time and Time Interval (PTTI) Meeting. Long Beach, Calif., 2001, pp. 359-369; and/or J. A. Dusters and C. A. Adams, “Performance requirements of communication base station time standards,” RF design, 28-38 (1999), the entire disclosures of which are incorporated herein by reference.
Quartz crystals oscillators, on one hand, are the most commonly used local frequency standard, but in many cases are not sufficiently accurate, have long term frequency drift, large size and high power consumption and relatively high cost, in the case of high performance quartz crystal oscillators, these drawbacks prevent them to be suitable for the above applications.
On the other hand Rubidium (Rb) or Cesium (Cs) gas base atomic clocks are highly accurate and they have high long-term frequency stability. However, the gas-based atomic clocks have large size, high power consumption, and high manufacturing cost.
U.S. Pat. No. 7,142,066 describes an atomic clock including substantially isolated particles that are capable of exhibiting hyperfine transitions. An alignment device of the clock may establish a predominant direction of spin of the particles. The clock may include an excitation device to, at regular intervals of time, cause the particles to undergo the hyperfine transitions by exciting the particles. A detection device of the clock may detect the hyperfine transitions of the particles. U.S. Pat. No. 7,030,704 describes a frequency standard that derives the reference frequency from the hyperfine spectrum of paramagnetic ions in solids.